Tonight, look for the faint constellation Ophiuchus the Serpent Bearer. From the Northern Hemisphere, look southward at nightfall. From the Southern Hemisphere, look more overhead around mid-evening. From all parts of Earth, Ophiuchus crosses the sky westward as Earth spins under the sky, and as evening deepens into late night. Ophiuchus is sometimes called the 13th or forgotten constellation of the zodiac.
The sun passes in front of Ophiuchus from about November 30 to December 18. And yet no one ever says they’re born when the sun is in Ophiuchus. That’s because Ophiuchus is a constellation – not a sign – of the zodiac.
What’s the difference? The 12 signs of the tropical zodiac represent equal 30 degree divisions of the sky, while the 13 constellations of the zodiac are of various sizes. The official constellation borders were agreed upon by the International Astronomical Union (IAU) in the early 20th century (1901 to 2000).
Read more: The Constellations by the IAU
That’s why, for example, the sun resides in front of each zodiacal sign for a precise interval of about a month. Meanwhile, the sun is in front of the constellations for varying amounts of time, for example, in front of the constellation Virgo for about 1 1/2 months and in front of constellation Scorpius for about a week.
The planet Jupiter and the bright red star Antares in the constellation Scorpius the Scorpion can help you find Ophiuchus in the night sky. Jupiter actually shines in front of Ophiuchus in 2019.
For the most part, Ophiuchus lies to the north of the star Antares. However, the southernmost part of Ophiuchus resides due east of Antares.
Even after Jupiter moves into different constellations of the zodiac in the years ahead, you can look for Ophiuchus a short hop to the north of Antares in any year. Ophiuchus’ brightest star – the 2nd-magnitude star called Rasalhague – highlights the head of Ophiuchus. (See Rasalhague in the Ophiuchus chart below.) It’s nowhere as bright as the planet Jupiter or the 1st-magnitude star Antares.
On sky maps, Ophiuchus the Serpent Bearer is depicted as holding Serpens the Serpent, which is considered a separate constellation. According to ancient Greek star lore, Ophiuchus is Asclepius, the physician who concocted a healing potion from the Serpent’s venom, mixing it with the Gorgon’s blood and an unknown herb. This potion gave humans access to immortality, until the god of the underworld appealed to Zeus to reconsider the ramifications of the death of death.
Even today, the Staff of Asclepius – the symbol of the World Heath Organization – pays tribute to the constellation Ophiuchus the Serpent Bearer.
Bottom line: Will you see faint Ophiuchus, the overlooked zodiacal constellation, tonight?
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.